Calculate Greenwich Mean Siderial Time at 0h, UT1 (GMST1) from UT1 year, month, and day.
1  gmst1(yr = 2012, mo = 1, dy = 1)

yr 
UT1 year (integer) 
mo 
UT1 month (integer) 
dy 
UT1 day (integer) 
Function calculates Greenwich Mean Siderial Time at 0h, UT1 (GMST1) given UT1 year, month, and day.
Returns fractional hours of GMST1 with class fracHrs. The
corresponding print method gives hh:mm:ss format rounded to n
decimal
places in seconds by setting options('digits.secs'=n)
.
Multiply UT1 fractional day by 1.002737909350795 to get fractional sidereal day.
Andrew Harris
Explanatory Supplement to the Astronomical Almanac Seidelmann (ed), c. 1992
ymd2jd
1 2 3 
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